Safety door latch



Dec.`26, 1961 G. c. ASHLEY SAFETY DOOR LATCH Filed Jan. 22. 1958 BUR/VER I N VEN TOR.

6 CASH@ BY MM United States Patent Office 3,014,440 Patented Dec. 26, 1961 States of America as represented by the Secretary of the Army Filed lan. 22, 1958, Ser. No. 710,591 4 Ciaims. (Cl. 110-179) (Granted under Title 35, U.S. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon.

This invention relates to safety means for blocking, unblocking, securing, latching, locking or fastening doors of furnaces, space heaters or fired vessels, and more especially pertains to securing means for a furnace or inciuerator door that has been closed and latched and which is only operative upon the occurrence of a predetermined thermal condition.

At present, there are conventional means for securing doors of tired furnaces or vessels which have the disadvantage of not being secured Iwhile the furnace is being tired with the disastrous result that under such hazardous conditions the furnace door may be opened by inexperienced or forgetful personnel resulting in an explosion or flashback causing destruction of property, serious harm or bodily injury by severe body burns to such personnel or may even result in the loss of life in some instances. This invention seeks to overcome these disastrous results and prevent serious bodily injury to operating personnel.

lt is a primary object of this invention to provide a simple and yet reliable apparatus operable only in response to a predetermined thermal condition to effectively secure the charging or observation doors of a tired furnace, space heater, and the like.

Another object of this invention is to provide a corrosion-resistant thermosensitive bimetallic strip which when subjected to variations in temperature bends to a predetermined position because of the different and dissimilar thermal expansion characteristics of the metals Y that comprise the composite strip or thermal element.

A further object of this invention is to provide a bimetallic element having temperature-responsive flexing properties suitable for securing the :latch means of a space heater door in response to a predetermined thermal condition.

The various novel structural features and arrangements contributing to the successful operation of the apparatus of the invention, and a more complete eX- position of its principles and mode of operation will be found Ain the following description and the accompanying drawings of the preferred embodiment thereof.

In the drawings- FIG. l is an elevational view partly in' section;

FlG. 2 is a horizontal section taken on line 2-2 of FIG. l; and

FIG. 3 is a detailed plan View of the metallic element in which the thermal element in latch securing condition is illustrated in full lines, and the element in the unsecured or cold furnace condition is illustrated by broken lines. l

In the preferred form of my invention it is intended that it shall be located within or adjacent to the combustion space of a furnace, spaceheater, incinerator, or similar tired device.

Referring to the drawings, FIG. l shows the assembly of my novel safety door latch as incorporated in a space hea-ter `lll which is fired by burner 11. Member 12 is an inspection door to which is fastened the gravity actuated latch mechanism comprising weighted handle 14,

hinge means 16, latch keeper 17, thermal element supportv 21 carrying in cantilever fashion thermal conductive element which in -turn serves by extension means as a support for bimetallic member 22. Door member 12 is attached by hinge means 13 to the wall of heater 10.

The thermal or radiation responsive element 22 is of laminated construction and comprises two relatively thin, elongated, `and longitudinal strips of metal of any suitable shape as illustrated by members 25 and 26 of FIG. 3 which may be fastened together by interfacial fusions, rivets, or by other suitable means, to provide a composite thermal rersponsive member 22. The two members 25 and 26 of member 22 should be formed or shaped as illustrated by member 22a in a bent arcuate shape for an unred furnace temperature condition as shown in FIG. 3 by dotted lines.

The two metal portions 25 and 26 of composite member 22 should be of dissimilar metals (such as Invar and low carbon steel or other desired dissimilar metals) hav- 'ing substantially differing coefficients of thermal expansion of such magnitude that composite thermal device 22 will straighten in longitudinal alignment due to unequal expansion of elements 25 and 26 when heated by the tiring of combustion chamber 3S, as shown by member 22 of FIGS. 2 and 3 in which straighened member 2.2 blocks the operation of latch keeper member 17 such that the furnace door 12 may not be opened during the firing of furnace 10 by burner 11. Member 22a, in broken lines of FIG. 3, illustrates the operative condition of member 22 in which it does not block member 17 when furnace 10 is not being fired, and the door 12 of furnace 10 may be opened without danger to operating personnel. While various metals, and possibly other materials, may be used for the component parts of the temperature or radiation responsive member 22, particularly satisfactory results have been obtained by the use of a strip 25 of low carbon steel of a certain thickness in combination with a strip 26 of lnvar of similar length, width, and thickness. Member 20 is of any suitable high thermal conductivity metal support means of a desired shape such as illustrated at 20, in FIG. 3, for the thermal responsive element 22 which is of any desired operational capacity and value for restoring the device to an operative condition, in the minimum possible interval of time following operation thereof. Member 20 may be of suitable hollow material to receive the thermally responsive element 22 in fixed position or may conceivably be a clamp, screwed or welded type holder for securing the thermally responsive element 22 in operating position as illustrated by FIG. 1.

While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obviousl to those skilled in the art that various changes and modifications may be made therein without departing from the invention.

I claim:

l. A heater device comprising a casing enclosing a combustion chamber, a door opening in said casing, a door operably secured over said opening, gravity actuated latch means pivotally and eccentrically carried by the door and having an external handle portion and an internally extending latch portion adapted to engage the inside surface portion of the combustion chamber,. U- shaped support means horizontally carried by the door and partially surrounding the internally extending por-tion of said gravity latch, and bi-element latch means mounted to extend from said support means in non-registering relation with said gravity actuated latch during non-tiring periods, said bi-element latch means being thermally responsive to move from the non-registering position to registering position with said gravity actuated latch during firing periods of high temperature.

2. A heater device comprising a casing enclosing a combustion chamber, a door opening in said casing, a door operably secured over said opening, gravity actuated latch means pivotally and eccentrically carried by the door and having an external handle portion and in internally extending latch portion adapted to engage the inside surface portion of the combustion chamber, a U- shaped support element horizontally carried by the door and substantially surrounding the internally extending portion of said gravity latch, and a cantilevered and thermally responsive latch securing means having a plurality of elements supported by and extending from said support means into the combustion chamber for selective engagement with said gravity latch during; conditions of elevated temperatures in the combustion chamber to prevent dis-engagement of the gravity latch With the inside surface of the combustion chamber, said thermally responsive latch securing means being selectively dis-engaged from said gravity latch during conditions of low temperatures in the combustion chamber permitting the door to be opened for access to the combustion chamber.

3. A heater device comprising a casing enclosing a combustion chamber, a door opening in said casing, a door operably secured over said opening, gravity actuated latch means pivotally and eccentrically carried by the door and having an external handle portion and an internally extending latch portion adapted to engage an inside surface portion of the combustion chamber, a U- shaped support element horizontally carried by the door and substantially surrounding the internally extending portion of said gravity latch and containing therein an aperture, and a safety detent securing latch means supported in the aperture in said U-shaped support and comprising a thermal conducting element connected at one end to said detent means to thermally actuate said detent means to extend in an arcuate path out of registry with said gravity actuated latch when in an unlocked condition of said gravity actuated latch during non-tiring periods of low temperature and to extend said detent means to an aligned horizontal position with said gravity actuated latch to secure and prevent actuation of said gravity latch during tiring periods of high temperature.

4. A heater device comprising a casing enclosing a combustion chamber, a door opening in said casing, a door operably secured over said opening, a gravity actuated horizontally pivoted latch lever means eccentrically carried by Ithe door with the externally extending handle portion integrally connected to a portion extending within the combustion chamber to engage the inside wall of the combustion chamber; a U-shaped support element carried by the door and substantially surrounding thc in-ternally extending portion of said gravity latch; and a cantilevered and temperature actuated latch securing bar having a plurality of elements supported by and extending from said support into the combustion chamber for selective engagement with said gravity latch during conditions of elevated temperatures in the combustion chamber to prevent disengament of the gravity latch and open- References Cited in the le of this patent UNITED STATES PATENTS 287,715 Porter Oct. 30, 1883 1,951,628 Prost Mar. 20, 1934 2,383,032 Abernethy Aug. 21, 1945 2,838,016 Sharpe Ian. 10, 1958 

